The invention relates to a motor vehicle with an internal combustion engine and an air conditioning system. The air conditioning system includes a compressor which is driven by an electric motor. This electric motor is also used as a starter for the internal combustion engine. A motor vehicle of this kind is, for example, known from US 2007/0187953 A1.
In addition to the clutch device, disclosed in the mentioned publication, for mechanically coupling the electric motor of the compressor of an air conditioning system with, for example, a crankshaft of the internal combustion engine, further clutch devices are known from the publications DE 199 31 963 A1 and DE 100 01 436 A1 for selectively coupling an electric motor with an internal combustion engine for a start of the internal combustion engine. Selectively is here to be understood as relating to a control signal that allows control as to when the clutch device mechanically couples the electric motor with the internal combustion engine and when it does not.
In the context of the invention, an internal combustion engine or a combustion engine is understood to be particularly an Otto engine, a diesel engine, or a Wankel engine. At the start of such an internal combustion engine, the electric motor, used as a starter, requires very much electrical current, which may, for example, be 1,000 amperes. A conventional starter system is powered by the low-voltage onboard electrical system of the motor vehicle. Low voltage is to be understood in the context of the invention as a voltage range between 0 volt and 60 volts. When using this starting system to start the internal combustion engine, the current must be provided from the low-voltage onboard electrical system. This leads to a voltage dip of the low-volt voltage, i.e. for example at 12 volt nominal voltage, this voltage may decrease to a value of less than 8 volts, or even 6 volts.
The low-voltage onboard electrical system also supplies safety-relevant consumers. This may involve, for example, headlights of the motor vehicle, the electronic stability program (ESP), an electrical steering assistance and/or a brake booster. As a result of the voltage dip caused by the start of the internal combustion engine, these safety-relevant consumers are in certain circumstances undersupplied so that they no longer fulfill their function. In the art, the provision of, for example, a power semiconductor is used as remedy which splits the low-voltage onboard electrical system in two parts. Accordingly, during starting procedure, a stable side is established with the rated voltage (e.g. 12 volts for a 12 volt onboard electrical system) for operation of the safety-relevant consumers. The starter is then supplied from a separate low-voltage battery.